Dual path current limiting circuit breaker



Sept. 17, 1968 0. JENSEN 3,402,272

DUAL PATH CURRENT LIMITING cmcun BREAKER Filed July 22, 1965 4 Sheets-Sheet 1 25 INVENTOR.

V77 JZ/VJi/V Sept. 17, 1968 O. JENSEN DUAL PATH CURRENT LIMITING CIRCUIT BREAKER Filed July 22. 1965 4 Sheets-Sheet 2 Sept. 17, 1968 o. JENSEN 3, 0

DUAL PATH CURRENT LIMITING CIRCUIT BREAKER Filed July 22, 1965 4 Sheets-Sheet 4 1 INVENTOR 477v JE/I/JF/V United States Patent 3,402,272 DUAL PATH CURRENT LIMITING CIRCUIT BREAKER Otto Jensen, Malvern, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed July 22, 1965, Ser. No. 474,006 4 Claims. (Cl. 200144) ABSTRACT OF THE DISCLOSURE A current limiting circuit breaker having a bridging main contact and a bridging arc contact carried in a movable insulation barrier. The main contact is disposed below the plane of main current flow, while the arcing contact is parallel to the plane of main current flow so high rate-of-rise-of-current tends to flow through the arcing contacts during fault conditions due to the inductance in the main contact path. A pair of arcing chambers are disposed on either side of the baflie and contain plates which have iron conductors connected in series by arcs extending between the plates in order to increase the resistance of the arc current path under interrupting conditions and to limit the current being interrupted.

This invention relates to circuit breakers, and more particularly relates to a novel circuit breaker construction which includes a pair of parallel arc chambers which cooperate with one another to force the arc in each to rise in its respective chamber wherein each of the chamhers are of the type which produce a solenoidal are current path which includes high temperature-resistivity coefiicient material as disclosed in my copending application Ser. No. 476,110, filed July 22, 1965, entitled Current Limiting Interrupter With Arc-Inserted Non-Linear Resistors," and assigned to the assignee of the present invention.

A principle object of this invention is to provide a novel circuit breaker having the characteristic of limiting the fault current to below some predetermined value.

Another object of this invention is to provide a novel circuit interrupter which limits fault current magnitude substantially below the available fault current of the circuit being protected and advances the occurrence of a current zero at which the fault will be interrupted.

Another object of this invention is to provide a novel circuit interrupter having current limiting characteristics thereby permitting the use of a smaller circuit breaker than heretofore was permissible.

These and other objects of this invention will become apparent from the following description when taken in connection with the drawings, in which:

FIGURE 1 is a front view of an arc interruptingplate of the type which may be used with the present invention.

FIGURE 2 is a bottom view of FIGURE 1.

FIGURE 3 is a side view of FIGURE 1.

FIGURE 4 is a top view of FIGURE 1.

FIGURE 5 is a cross-sectional view of FIGURE 1 taken across the line 5-5 in FIGURE 1.

FIGURE 6 schematically illustrates the stacking of plates similar to that of FIGURE 1 with respect to one another to define an arc chute.

FIGURE 7 illustrates the V-shaped conductors in the arc chute of FIGURE 6 to illustrate the formation of a solenoidal current path.

FIGURE 8 is a side plan view of a dual arc chute constructed in accordance with the present invention.

FIGURE 9 is a cross-sectional view of FIGURE 8 taken across the line 9-9 in FIGURE 8.

FIGURE 10 is a plan view of the contact carrier which is introduced into the arc chute of FIGURE '8.

FIGURE 11 is a schematic cross-sectional view of the arc chute of FIGURE 9 taken along the line 1111 in FIGURE 9, in combination with the circuit breaker contact structure with the contacts in the closed position.

FIGURE 12 is similar to FIGURE 11, and illustrates the contacts in their open position.

FIGURE 13 is a diagram of the various circuit variables of the system of FIGURES 11 and 12 as plotted against time, particularly to illustrate the reduced fault current to which the circuit interrupter is exposed.

Referring first to FIGURES 1 through 7, I have illustrated therein the type of arc chute which is used in the dual arc chute device of the present invention, and which is illustrated in my copending application Ser. No. 474,110.

Referring first to FIGURES 1 through 5, I have illustrated therein a typical plate and V-shaped conductor which could be used directly in the arc chamber of the type shown in US. Patent 2,353,729. More specifically, FIGURES 1 through 5 illustrate a ceramic plate 10 which has headed edges 11 and 12. A V-shaped conductor 13 which is made of a flat strip of high resistivity-temperature coefiicient material is then provided with two extending legs 14 and 15 which straddle the plate 10, and are nested within the side beads 11 and 12, respectively, of the plate 10. Note that each of legs 14 and 15 have a tapered cross-section which decreases from the bottom of the V-shaped conductor 13 toward the top thereof.

The V-shaped conductor 13 is then made of a high resistivity-temperature coefiicient material such as pure iron or tungsten.

It is to be noted that by a high resistivity-temperature coefiicient, I refer to a material which has a resistivitytemperature coefiicient which will provide at least a tenfold change in resistance from a cold temperature, or room temperature, to are current temperatures, or hot temperature.

Arcing tips of some suitable arc-resisting material such as tungsten are then placed on the upper ends of the V-shaped conductor shown as tungsten arcing tips 16 and 17, respectively. The manner in which the arcing tips 16 and 17 are applied to the pure iron V-shaped conductor is well known to those skilled in the art, and, for example, the tips can be welded to the iron body.

An interrupting chamber may then be formed by stacking the plates shown in FIGURES 1 through 5 in parallel spaced relation with respect to one another in any desired manner such as the manner disclosed in the above noted US. Patent 2,353,729. For purposes of illustration, FIG- URE 6 illustrates a plurality of plate assemblies 20 through 24 which are terminated by ceramic end plates 25 and 26 in an exploded perspective view, particularly to illustrate the parallel disposition of the various plates each of which are of the type shown in FIGURES 1 through 5.

A pair of cooperating contacts are schematically illustrated in FIGURE 6 as contacts 27 and 28 which are connected to terminals 29 and 30, respectively. FIGURE 6 further illustrates in a schematic fashion the connection of terminals 29 and 30 to the conductors of the end plates 20 and 24, respectively, whereupon when the contacts 27 and 28 are opened, the arc of these contacts is connected in series with the various plates.

The solenoidal behavior of the arc is schematically illustrated in FIGURE 7 which shows the conductive plates in the absence of their respective ceramic spacers. Thus FIGURE 7 illustrates four adjacent V-shaped conductors 31a-31b, 32a-32b, 33a-33b and 34a34b. Note that each of V-shaped conductors 31 through 34 are identical to the conductor 13 of FIGURES 1 through 5, and that the legs of the conductors are terminated by a suitable arc-resistant material.

It will be further observed that the legs 31a and 32b are coplanar, and are spaced from one another in air between the ceramic plates which are straddled by conductors 31 and 32. In a similar manner, legs 32a and 33b will be coplanar, while legs 33a and 34b will be coplanar.

Assuming now that an arc has been suitably introduced into the arc chamber, the initial current path will be the solenoidal path shown in dotted lines in FIGURE 7. That is to say, the arc will initially fiow into the bottom of leg 31b and thence upwardly in leg 31a. Thereafter, there is an arc from leg 31a over to the coplanar spaced leg 32b, as illustrated in dotted lines, with the current path then going down in leg 32]; and up leg 32a into the next are from leg 32a to its coplanar leg 33b.

By following this initial current path, it will be seen that the current path is solenoidal so that a magnetic field is generated in the solenoidal current path tending to cause the solenoid diameter to expand. This causes the arc roots on the inner edges of the various legs of plates 31 through 34 to move upwardly until the arc finally roots at the top of each of the legs, as shown by the jagged line suggestive of the arc.

Once again, the self-inductance of the solenoidal current path tends to cause the arcs at the tops of the coplanar legs to expand upwardly, thereby stretching and cooling the arc. Note that these arcs root upon the areresistant ends of the various legs.

Moreover, and since the material of plates 31 through 34 was selected to be of a high resistivity-temperature coeflicient material, as current flows through the legs, its

temperature and thus its resistance is gradually increased, thereby gradually introducing an increasing resistance into the faulted circuit. Moreover, and since the crosssectional area of the various legs decreases as the arc moves upwardly, there will be a still further gradual increase in the resistance of the solenoidal current path.

All these elfects of the novel construction contribute to cause a gradual increasing resistance into the solenoidal current path to avoid the appearance of a high induced voltage across the solenoidal current path.

Moreover, the novel construction of the high resistance leg extensions in the form of fiat strips speeds the cooling of the metallic legs after the arc is successfully interrupted.

FIGURES 8 through 12 illustrate the manner in which the type of arc plate shown in FIGURES 1 through 7 is utilized in accordance with the invention.

More particularly, and in accordance with the invention, the dual arc chute is composed of a pair of opposing arc chutes 45 and 46 each similar to the arc chutes of FIG- URES 1 through 6. Each of the arc chutes 45 and 46 are provided with suitable arc runners 50 and 52, respectively, which are electrically connected to one another (not shown).

A pair of insulation end plates 53 and 54 then are suitably secured to the sides of plates 47 and 48 as by screws or the like to complete a hollow square enclosure. The various plates for defining the interrupter chamber are then rigidly secured to plates 47 and 48 by side mounting, wherein the opposing surfaces of plates 47 and 48 may be slotted to receive the side edges of the various plates, thereby to hold them rigidly in position with respect to one another.

Thus, in FIGURES 9, 11 and 12, the plates 55 and 56 which carry their respective V-shaped conductors of high temperature-resistivity coeflicient material are rigidly supported in suitable slots in the side walls 47 and 48. Note that the plates 55 and 56 of FIGURES 9, 11 and 12 differ somewhat from those of FIGURES 1 through 7 in that the top of the plates are square rather than rounded, although the rounded plate can be used with suitably rounded enclosing members 53 and 54.

The plates 47 and 48 have a further pair of opposing notches therein such as notches 60 and 61 which carry a movable insulation barrier 62 which may be of any suitable insulation material such as polytetrafluoroethylene known by the trademark Teflon. The barrier 62 then has embedded therein two bridging contacts; a bridging arcing contact 63 and a bridging main contact 64 wherein main contact 64 is of some high conductivity material such as silver or copper, while arcing contact 63 is made of, or is coated with some suitable arc-resistant material such as tungsten.

It will be seen that the housing of FIGURES 3 and 9 defines two parallel interrupting chambers. That is to say, the plates on either side of barrier 62 define a single complete chamber which will form a solenoidal-shaped current path which includes an arc section and a metallic section wherein the resistance of the metallic section gradually increases as the temperature of the plates increase.

This dual housing is then mounted atop a main contact structure and secured thereto in any desired manner, as illustrated in FIGURES 11 and 12. Thus, in FIGURES 11 and 12, the contact structure is comprised of a pair of co-linear contact legs and 71 which include main stationary contact sections 72 and 73, respectively, and stationary arcing contact plates 74 and 75, respectively. The stationary contacts 70 and 71 are so arranged that the main contacts 72 and 73 which are of soft, high conductivity material are disposed below the plane of the conductors 70' and 71. That is to say, the main current flow through the contacts, as shown by arrows 7'6, 77, 78, 79 and '80 is depressed below the straight flow of current, illustrated by arrows 81 and 82, through the arcing contacts 74, 7'5 and the bridging arcing contact 63. A complete circuit is then formed, as illustrated, for example, in FIGURE 11 by connecting a suitable A-C source 83 and a load 84 (which is to protected), in series with contact legs or terminals 70 and 71.

The function of the main contacts 72, 73 and their bridging contact 64 is to conduct the normal current of load 84. Thus, these contacts are relatively massive so as to constitute a heat sink for the heat generated by the current flow in the moving contact. At the same time, however, the mass of movable contacts 63 and 64 and the barrier 62 are made to be relatively light in weight so that it may be rapidly accelerated by reasonable operating forces.

Thus, the arrangement may have an operating mechanism 90, schematically illustrated in FIGURE 8, as connected to the barrier 62 which may be of the high-speed operating type disclosed in US. Patent 2,916,579 in the names of Kesselring and Diebold.

In order to interrupt the circuit, the barrier 62 is moved from the closed position of FIGURE 11 to the open position of FIGURE 12 with relatively high speed by virtue of the low mass of the movable assembly.

The arrangement whereby the main contacts 72 and 73 are disposed below the arcing contacts 74 and constitute one of the distinctive features of the present invention. Thus, the arcing contacts 74 and 75 are co-linear with the circuit breaker terminals 70 and 71, while the main contacts 72 and 73 are disposed beneath this line. This causes the current path through main contacts 72 and 73 to have a greater inductance than the path through arcing contacts 74 and 75 whereby during interruption of fault currents having a high rate of rise of current, the difference in inductance diverts current flow toward the arcing contacts thereby minimizing the current to be opened by the main contacts and the consequent erosion of the main contacts. However, during normal operation, the effect of this additional inductance is negligible so that current flow is diverted toward the lower resistance path ottered by main contacts 72 and 73.

When the circuit breaker is opened by the upward movement of barrier 62, the moving contact 64 and then the arcing contact '63 open in succession by virtue of their different lengths. Arcs are then drawn on both sides of barrier 62 at the instant when movable arcing contact 63 separates from its stationary contacts 74 and 75.

As the barrier continues to move upwardly, these two arcs are elongated with the current in these two arcs flowing in opposite directions. The oppositely flowing arc currents repel one another, thereby forcing them into the respective interrupting chambers on the opposite sides of the barrier 62. This arrangement for moving the arcs into their respective interrupting chambers constitutes a further distinctive feature of the invention.

Once the arcs move into their respective chambers, they are broken into separate segments which are connected in series with a solenoidal configuration as described, for example, in FIGURE 7. Moreover, and in accordance with the invention, the magnetomotive forces of these two solenoidal current paths which are parallel to one another are additive.

The solenoidal arc current in the two halves of the interrupter are then each respectively limited by the resistance of their high temperature-resistivity coefficient material conductors in the arc chute, thereby producing an increase in the total are path resistance and a subsequent reduction in current. Moreover, this increase in resistance is relatively gradual, thereby avoiding the generation of high self-induce voltages in the circuit inductance.

The current limiting action of this arrangement is best understood by reference to FIGURE 13 which illustrates the circuit voltage or the voltage of source 83; the resistance value or the effective resistance of the V-shaped conductors in the two are chutes; the actual current flow in the arc; and the available fault current or the current which would fiow in the absence of the increasing arc resistance.

Thus, FIGURE 13 illustrates the fault inception at time t At time 1 any desired fault indicating equipment measures the existence of a fault condition, and by time t the operating mechanism has begun to move the barrier 62 upwardly. From times t to t the are drawn from the contact 63 to its cooperating contacts 74 and 75 moves into the arc chute and travels along the V- shaped conductors thereby inserting their resistance in the circuit. In the time interval t to 12,, the V-shaped conductors continue to be heated, and thus continue to increase their resistance, whereby the actual current fiowing through the arc is the current labeled as reduced current which has decreased to zero by time t It should be particularly noted that the current Zero is reached in FIGURE 13 at or near a voltage zero so that at this instant there is substantially Zero power applied across the open contacts.

It is of particular significance that the area under the actual reduced current which flows through the circuit breaker of the invention is considerably smaller than that beneath the available fault current curve, thus indicating the substantial reduction of power required to be interrupted by the novel interrupter of the invention.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many modifications and variations will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A current limiting circuit breaker comprising first and second terminal conductors ha'ving spaced opposing ends; first and second respective main stationary contacts and first and second respective stationary arcing contacts connected to the said opposing ends of said first and second spaced terminal conductors; an elongated movable insulation barrier plate movable in the direction of its said elongation; a bridging main contact and a bridging arcing contact each connected to said movable insulation barrier plate, and extending through said barrier plate and spaced from one another along the direction of motion of said barrier plate; each of said first and second main stationary contacts and first and second stationary arcing contacts, respectively, spaced from one another on the said ends of said first and second terminal conductors by a distance approximately equal to the spacing of said bridging main contact and bridging stationary contact; said barrier plate interposed between said opposing ends of said first and second terminal conductors; said bridging main contact and bridging arcing contact in succession simultaneously engaging said first and second main contacts and said first and second arcing contacts, respectively, when said circuit breaker is closed and moving to respective disengaged positions responsive to movement of said barrier plate in its said direction of elongation to open said circuit breaker; said first and second terminal conductors including co-linear portions; said first and second stationary arcing contacts being aligned with said co-linear portions; said first and second main stationary contacts being displaced below the line of said co-linear portions whereby current flow from said first terminal conductor to said first stationary main contact to said main movable contact to said second stationary main contact is a generally V-shaped path having a greater inductance than the generally linear path including said first and second terminal conductors, said first and second stationary arcing contact and said movable arcing contact.

2. A current limiting circuit breaker comprising first and second terminal conductors having spaced opposing ends; first and second respective main stationary contacts and first and second respective stationary arcing contacts connected to the said opposing ends of said first and second spaced terminal conductors; an elongated movable insulation barrier plate movable in the direction of its said elongation; a bridging main contact and a bridging arcing contact each connected to said movable insulation barrier plate, and extending through said barrier plate and spaced from one another along the direction of motion of said barrier plate; each of said first and second main stationary contacts and first and second stationary arcing contacts, respectively, spaced from one another on the said ends of said first and second terminal conductors by a distance approximately equal to the spacing of said bridging main contact and bridging stationary contact; said barrier plate interposed between said opposing ends of said first and second terminal conductors; said bridging main contact and bridging arcing contact in succession simultaneously engaging said first and second main contacts and said first and second arcing contacts, respectively, when said circuit breaker is closed and moving to respective disengaged positions responsive to movement of said barrier plate in its said direction of elongation to open said circuit breaker; and a first and second interrupter chamber; said first and second interrupter chambers mounted on opposite sides of said barrier plate and receiving arcs drawn from said bridging arcing contact to said first and second stationary arcing contacts, respectively; said bridging arcing contact moving between said first and second interrupter chambers responsive to movement of said barrier plate in its said direction of elongation.

3. The device as set forth in claim v2 wherein said first and second terminal conductors include co-linear portions; said first and second stationary arcing contacts being aligned with said co-linear portions; said first and second main stationary contacts being displaced below the line of said co-linear portions where by current flow from said first terminal conductor to said first stationary main contact to said main movable contact to said second stationary main contact is a generally V-shaped path having a greater inductance than the generally linear path including said first and second terminal conductors, said first and second stationary arcing contact and said movable arcing contact.

4. The device as set forth in claim 2 wherein each of said first and second interrupter chambers are identical in construction and include a plurality of spaced arc plates; each of said are plates comprising a flat elongated plate of insulation material and a generally V- shaped conductive member; said generally V-shaped conductive member comprising a first and second leg formed at an apex; said first and second legs disposed in spaced parallel planes; said first and second legs straddling the bottom of said elongated plate and extending upwardly in contact with the respective opposing surfaces of said elongated plate along opposite lateral surfaces of said plate; said generally V-shaped conductive member being comprised of a high resistiw'ty-temperature coefiicient material characterized by attaining a hot resistance of approximately ten times the cold resistance thereof wherein said cold resistance is its resistance at room temperature and said hot resistance is the resistance thereof when are currents flow through said material.

References Cited UNITED STATES PATENTS 1,963,760 6/1934 Pittman et a1 200151 2,538,370 1/ 1951 Lerstrup 200--147 2,629,036 2/1953 Brown 200147 2,764,652 9/ 1 956 Debuit 200-146 3,128,361 4/1964 Kesselring 200-15l FOREIGN PATENTS 1,252,489 12/ 1960 France.

15 ROBERT S. MACON, Primary Examiner. 

